There already exist known metallurgical treatments in molten baths--for instance ductile iron--which use as the reaction material pure magnesium, or its alloys, which is vaporized in the molten bath to obtain spheroidal graphite and modifications thereof, or for desulphurization, deoxidation or similar treatments.
Using traditional techniques, vaporization is obtained by means of direct contact between the reaction material and the molten metal. The required quantity of reaction material is placed directly in the molten metal and heated and vaporized by it. The supply of reaction material and the metallurgical treatment are generally discontinuous, and also involve significant loss of vapor and deformities of the bath treatment.
Known methods currently used for cast iron, particularly those using pure metallic magnesium at atmospheric or metallostatic pressure, have an efficiency or no more than 60%; virtually 40% of the reagent fed into the bath is lost in the form of fumes and heat. The reason for this lies in the production of vapor, which is discontinuous with irregular peaks of high pressure generated when the liquid or solid reagent comes into contact with the molten metal.
Various methods have been designed to reduce this loss and the resulting environmental impact, some of which also envisage continuous treatment of the metal flow as shown in CH-A43993599. Document CH-A-382783 discloses the possibility of improving the technology by using a continuous process of feeding the reagent material in the form of a wire into a pressurized bell immersed in a molten bath. However, the continuous distribution described here does not allow constant vaporization because when the liquid/solid reagent comes into direct contact with the molten bath, it causes cooling and consequently halts vaporization, and hence the stated aims are not attained.
More recently, a method of metallurgical treatment in a molten bath has been proposed. The molten bath is of a vaporizable reaction material in which the reaction material is placed in at least one chamber, immersed in the molten metal and vaporized without direct contact with the metal. In effect, the reaction material is heated and vaporized through the walls of the chamber and the vapor produced is conveyed out of the chamber towards the molten metal.
However, this method too is discontinuous although it provides some advantages in the use and distribution of vapor in the molten metal for a more homogenous treatment.
In other words, metallurgical treatments conducted with known methods are discontinuous considering the discontinuous supply of reaction material. On the other hand, for some treatments, apart from the vaporizable material it is necessary to have inoculating or refining material for the bath. Metering and delivery to the bath of these materials are generally effected by simple addition during transfer of the metal and cause oxidation and the formation of residue leading to defects in the castings produced.